Thanks for the paper! I couldn't find [mvcf~] in the ekext deken package but there is a [lpreson~], are these somehow related? Anyway, I will compile [mvcf~] from source and listen to it :-).
Gesendet: Montag, 17. Oktober 2016 um 12:49 Uhr Von: "Ed Kelly" <[email protected]> An: "Alexandre Torres Porres" <[email protected]>, "Christof Ressi" <[email protected]> Cc: pd-list <[email protected]> Betreff: Re: [PD] could vanilla borrow iemlib's hi pass filter recipe? Hey people, While I'm not an expert with digital filters, I did manage to piece together a decent-sounding ladder emulation instead of vcf~ a while ago. It only does resonant lowpass though. It's called mvcf~ and is found in the ekext externals library. I've since been reading about analogue filter design and I reckon there may be high pass and band pass filters available from the source code, with the correct adjustment to the algorithm. I'm trying to work out how to adjust the coefficients to accurately model the alternative functions (i.e. highpass, and hence bandpass through arithmetic processes) according to the resistance factors outlined in this paper. Any help would be appreciated :) So, currently, at line 78 in the code I have translations for highpass and bandpass (the current implementation is lowpass only with a gain factor) but I may be stupid in not trying this myself (or I've just been super-busy with other stuff - I'm marking this week). The idea of implementing the other two modes comes from an Electronotes paper from Bernie Hutchins in the 1970s. http://electronotes.netfirms.com/EN85VCF.PDF Take a look. Cheers, Ed PS have yet to try bob~ but it sounds interesting...will check it out. On Sunday, 16 October 2016, 13:10, Alexandre Torres Porres <[email protected]> wrote: > But [bp~] and [vcf~] are almost unusable IMHO and should probably be replaced > by better filters in the future (while keeping the old ones for compatibility > reasons). how about bob~? 2016-10-14 21:34 GMT-03:00 Christof Ressi <[email protected][mailto:[email protected]]>:There are a number of big problems with all build-in filters in Pd (expect for the raw filters). Problem number 1: [lop~] and [hip~] both use a weird (you could also say: wrong) formula for the cutoff frequency which makes them gradually converge to a fixed output state (reached by about 7000 Hz). The same is true for [vcf~] and [bp~] with Q <= 1. Therefore the actual cutoff frequency is only correct for very low frequencies and approximately gets more and more off until it doesn't move at all. Problem number 2: [bp~] and [vcf~] don't have zeros at DC and Nyquist. For low Q values, the slope is different for each side and changes with frequency. Problem number 3: the gain at the center frequency is not 1 for both [bp~] and [vcf~]. It rather depends on frequency and Q. [bp~] even has has a gain of 2 for Q <= 1! I did some FFT plots, see the attachment. I remember Miller saying somewhere that these filters are not designed for high cutoff frequencies - but even for low frequencies, the behaviour of [bp~] and [vcf~] is horrible. I can see these filters are mere approximations to reduce CPU usage. [hip~] is indeed much more efficient than iemlib's [hp1~], so it's well suited for DC removal (but not much else). [bp~] only is a little bit more CPU friendly than iemlib's [bp2~] - but the latter one has a correct and stable frequency response. [vcf~], however, is a real CPU sucker!!! 100 [vcf~] objects need 3,40% on my laptop whereas 100 of iemlib's [vcf_bp2~] only need 1,80%! But you have to consider that [vcf_bp2~] not only acts correctly but lets you set the Q at audio rate. The high CPU usage of [vcf~] seems like a bug to me... I only use the vanilla filters for the most basic stuff like DC removal and smoothing. I guess these are the use cases which Miller had in mind and that way [lop~] and [hip~] have their justification (although there should be some more warning about the 'wrong' frequency response in the help file). But [bp~] and [vcf~] are almost unusable IMHO and should probably be replaced by better filters in the future (while keeping the old ones for compatibility reasons). Christof > Gesendet: Freitag, 14. Oktober 2016 um 23:51 Uhr > Von: katja <[email protected][mailto:[email protected]]> > An: pd-list <[email protected][mailto:[email protected]]> > Betreff: [PD] could vanilla borrow iemlib's hi pass filter recipe? > > In pd 0.47.1 [hip~] is still not perfect. Attenuation at cutoff is not > constant over the frequency range: -6 dB with cutoff=SR/8, -3 dB with > cutoff=SR/4, 0 DB with cutoff=SR/2. In contrast, iemlib's [hp1~] has > -3 dB at cutoff consistently. > > Could vanilla pd implement iemlib's hipass filter recipe? I don't know > if the license also covers the math. Documentation in > https://git.iem.at/pd/iemlib/ > tree/master[https://git.iem.at/pd/iemlib/tree/master] points to external > literature > for part of the math (bilinear transform). I've implemented the recipe > with vanilla objects for comparison, see attached. > > Katja> ______________________________ _________________ > [email protected][mailto:[email protected]] mailing list > UNSUBSCRIBE and account-management -> https://lists.puredata.info/ > listinfo/pd-list[https://lists.puredata.info/listinfo/pd-list] > ______________________________ _________________ [email protected][mailto:[email protected]] mailing list UNSUBSCRIBE and account-management -> https://lists.puredata.info/ listinfo/pd-list[https://lists.puredata.info/listinfo/pd-list] _______________________________________________ [email protected][mailto:[email protected]] mailing list UNSUBSCRIBE and account-management -> https://lists.puredata.info/listinfo/pd-list[https://lists.puredata.info/listinfo/pd-list] _______________________________________________ [email protected] mailing list UNSUBSCRIBE and account-management -> https://lists.puredata.info/listinfo/pd-list
